1. Technical Field of the Invention
The present invention relates to a data separation and decoding device suitable for a set top box (STB) utilized in recording digital broadcasts such as satellite broadcasts, in particular, to a data separation and decoding device for allowing multiplexing of a digital signal.
2. Description of the Related Art
Recently, an MPEG (Motion Picture Coding Experts Group) 2 standard has been adopted for compression of moving image data in broadcasting systems for multi-channel digital broadcasts, in DVDs, or the like. According to the MPEG2 standard, two types of streams, a transport stream (TS) and a program stream (PS), are specified as signals wherein a plurality of contents, such as video content, audio content, and the like, are multiplexed and, in particular, a transport stream is utilized in digital broadcasts. A transport stream is formed of sequential packets, which are referred to as TS packets. One TS packet is formed of a four byte packet header, provided at the front, as well as a 184 byte adaptation field and/or a payload provided following the packet header. That is to say, the number of bytes of a TS packet is 188 bytes. In addition, a packet header includes an eight bit synchronous byte, a 13 bit packet ID, and the like. Furthermore, the adaptation fields of some of the TS packets include a PCR (Program Clock Reference) that indicates information concerning the relative transmission time of these TS packets.
In addition, recently, transport streams of a plurality of channels have come to be simultaneously transmitted in digital broadcasts. FIG. 1 is a block diagram showing a conventional data separation and decoding device. Conventional data separation and decoding device 101 is provided with separation and decoding circuits 102-1 to 102-n (n : natural number) in the same number as the number of channels of the transport streams. Transport streams TS#1 to TS#n, respectively, are inputted to separation and decoding circuits 102-1 to 102-n. Then, separation (filtering) of TS packets and descrambling are carried out by each of the separation and decoding circuits based on the packet ID included in the packet header of the TS packet. An external memory interface (I/F) circuit 103 is provided at the rear stage of separation and decoding circuits 102-1 to 102-n so that the separated and decoded stream outputted from each of the separation and decoding circuits 102-1 to 102-n is inputted to this external memory I/F circuit 103. External memory I/F circuit 103 selects one separated and decoded stream based on a command from the outside so as to output it to a memory.
Data separation and decoding device 101 according to a prior art having the above described configuration makes it possible to store, in a memory, data of a program that has been arbitrarily selected for transport streams of a plurality of channels.
However, there are problems wherein the scale of the separation and decoding circuits is comparatively large and wherein such separation and decoding circuits are provided in the same number as the number of channels of the transport streams and, therefore, the scale of the entire device becomes large.